Police are investigating a fraud in which someone put rocks in iPod packages and exchanged the packages for new MP3 players.

On Jan. 3, someone exchanged two iPods for four Microsoft Zune MP3 players at the south Wal-Mart Supercenter, 8700 Andermatt Drive, said Officer Katie Flood.

It looked like the iPods had never been opened, but police now believe someone was able to use heat to reseal the plastic packaging, Flood said.

A customer who bought one of the returned iPods the next day discovered a rock in the box, Flood said. The total loss was $530.46.

The suspect or suspects may have left in a red Chevrolet Impala, Flood said. Police believe other Wal-Marts along the Interstate 80 corridor have fallen victim to this scam.